1. Field of the Invention
This invention relates to novel 3,4,5-trisubstituted aryl nitrone compounds and their use as therapeutic agents for the treatment of inflammation-related conditions in mammals, such as arthritis, and as analytical reagents for detecting flee radicals.
2. State of the Art
Arthritis and related inflammatory disease conditions occur in more than 100 different forms, including rheumatoid arthritis (RA), osteoarthritis (OA), ankylosing spondylitis and systemic lupus erythematosus (SLE). Most forms of arthritis are characterized by some type of chronic inflammation. For example, RA typically involves chronic inflammation of the lining of the joints and/or the internal organs. Such chronic inflammation generally causes pain and swelling in the joints of those afflicted and may result in damage to cartilage, bone, tendons, ligaments and the like, ultimately leading to deformity and disability.
Prostaglandins have long been known to be involved in the inflammation process. Accordingly, a number of inhibitors of prostaglandin synthesis have been developed for the treatment of arthritis and related inflammatory disease conditions. Such non-steroidal antiinflammatory drugs (NSAIDS), such as aspirin, ibuprofen, naproxen and indomethacin, typically prevent the production of prostaglandins by inhibiting enzymes in the arachidonic acid/prostaglandin pathway, including the enzyme cycloxygenase (COX). The enzyme COX catalyzes the conversion of arachidonic acid to prostaglandin H2, the first step in the biosynthesis of prostaulandins such as prostacyclin and thromboxanes. The enzyme COX is now known to exist in two forms. COX-1 is a constitutive form of the enzyme found in most tissues and organs. Among other properties, COX-1 produces relatively small amounts of prostoglandins necessary for maintaining the integrity of the gastrointestinal tract. COX-2, on the other hand, is an inducible form of the enzyme associated with the increased production of prostoglandins during inflammatory conditions. Since many NSAIDS inhibit both forms of COX, they interfere with prostaglandin-regulated processes not associated with the inflammation process. As a result, many NSAIDS cause severe side effects, such as stomach ulcers and renal damage, which limit their effectiveness as therapeutics.
Accordingly, a need exists for novel classes of therapeutic compounds which effectively treat arthritis and other inflammation-related conditions without producing undesired side effects.
This invention provides novel 3,4,5-trisubstituted aryl nitrone compounds which are useful as therapeutics for reducing inflammation in mammals. In particular, the compounds of this invention are useful for treating arthritis and other inflammation-related conditions.
Accordingly, in one of its composition aspects, this invention is directed to compounds of formula I: 
wherein
R1 is selected from the group consisting of: 
each R2 is independently selected from a group of the formula: 
R3 is selected from the group consisting of hydrogen, alkyl, cycloalkyl and aryl;
R4 is selected from the group consisting of alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, cycloalkyl, substituted cycloalkyl, cycloalkenyl and substituted cycloalkenyl;
R5 is selected from the group consisting of alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, cycloalkyl, substituted cycloalkyl, cycloalkenyl and substituted cycloalkenyl;
R6 and R7 are independently selected from the group consisting of hydrogen, alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, cycloalkyl, substituted cycloalkyl, cycloalkenyl and substituted cycloalkenyl; or R6 and R7 can be joined to form an alkylene or substituted alkylene group having from 2 to 10 carbon atoms;
R8 is selected from the group consisting of alkyl, substituted alkyl, alkenlyl, substituted alkenyl, alkynyl, substituted alkynyl, cycloalkyl, substituted cycloalkyl, cycloalkenyl and substituted cycloalkenyl;
R9 is selected from the group consisting of hydrogen, alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, cycloalkyl, substituted cycloalkyl, cycloalkenyl and substituted cycloalkenyl; or R8 and R9 can be joined to form an alkylene or substituted alkylene group having from 2 to 10 carbon atoms;
R10 is selected from the group consisting of hydrogen, lower alkyl and lower cycloalkyl; or R1 and R10 can be joined to form an alkylene, substituted alkylene, xe2x80x94C(O)xe2x80x94xe2x80x94S(O)xe2x80x94 or xe2x80x94S(O)2xe2x80x94 group;
R11 and R12 are independently selected from the group consisting of lower alkyl and lower cycloalkyl; or R11 and R12 can be joined to form an alkylene group having from 2 to 10 carbon atoms;
X is oxygen, sulfur, xe2x80x94S(O)xe2x80x94 or xe2x80x94S(O)2xe2x80x94; and
W is oxygen or sulfur; and pharmaceutically-acceptable salts thereof.
Preferably, R3 is hydrogen or lower alkyl. More preferably, R3 is hydrogen or alkyl having 1 to 4 carbon atoms, more preferably 1 or 2 carbon atoms. Still more preferably, R3 is hydrogen.
R4 is preferably selected from the group consisting of alkyl, substituted alkyl and cycloalkyl. More preferably, R4 is alkyl having 3 to 6 carbon atoms or cycloalkyl having 5 to 6 carbon atoms. Particularly preferred R4 groups include methyl, n-propyl, isopropyl, 1-hydroxy-2-methylprop-2-yl, n-butyl, tert-butyl, 3-thiomethylpropyl, 3-(thiomethoxy)but-1-yl, cyclohexyl, 4-trifluoromethybenzyl and 3,4,5-trimethoxybenzyl.
R5 is preferably selected from the group consisting of alkyl and cycloalkyl. More preferably, R5 is lower alkyl. Particularly preferred R5 groups include methyl, ethyl, n-propyl, isopropyl and n-butyl.
R6 is preferably selected from the group consisting of alkyl and allkoxycarbonylalkyl (i.e., ROC(O)-alkyl-, where R is alkyl or cycloalkyl). Particularly preferred R6 groups include ethyl, n-propyl, isopropyl, n-butyl, ethoxycarbonylmethyl and 2-(ethoxycarbonyl)ethyl. R7 is preferably hydrogen.
Preferably, R8 is alkyl or alkoxyalkyl (i.e., RO-alkyl-, where R is alkyl). Particularly preferred R8 groups include methyl and methoxyethyl. R9 is preferably hydrogen. Preferably, X is oxygen.
Preferably, R10, R11 and R12 are independently lower alkyl. More preferably, R10, R11 and R12 are methyl.
W is preferably oxygen.
In a preferred embodiment, this invention is directed to a compound of formula II: 
wherein
R13 is selected from the group consisting of alkyl, substituted alkyl, cycloalkyl and substituted cycloalkyl;
R14 is selected from the group consisting of alkyl, substituted alkyl, cycloalkyl and substituted cycloalkyl; and pharmaceutically-acceptable salts thereof.
Preferably, R13 is lower alkyl.
R14 is preferably selected from the group consisting of alkyl, substituted alkyl and cycloalkyl. More preferably, R14 is alkyl having 3 to 6 carbon atoms or cycloalkyl having 5 to 6 carbon atoms. Particularly preferred R14 groups include methyl, n-propyl, isopropyl, 1-hydroxy-2-methylprop-2-yl, n-butyl, tert-butyl, 3-thiomethylpropyl, 3-(thiomethoxy)but-1-yl, cyclohexyl, 4-trifluoromethybenzyl and 3,4,5-trimethoxybenzyl.
In another preferred embodiment, this invention is directed to a compound of formula III: 
wherein
R15 and R16 are independently selected from the group consisting of hydrogen alkyl, substituted alkyl, cycloalkyl, substituted cycloalkyl; or R15 and R16 can be joined to form an alkylene or substituted alkylene group having from 2 to 10 carbon atoms;
R17 is selected from the group consisting of alkyl, substituted alkyl, cycloalkyl and substituted cycloalkyl; and pharmaceutically-acceptable salts thereof.
R15 is preferably selected from the group consisting of alkyl and alkoxycarbonylalkyl (i.e., ROC(O)-alkyl-, where R is alkyl or cycloalkyl). Particularly preferred R15 groups include ethyl, n-propyl, isopropyl, n-butyl, ethoxycarbonylmethyl and 2-(ethoxycarbonyl)ethyl. R16 is preferably hydrogen.
R17 is preferably selected from the group consisting of alkyl, substituted alkyl and cycloalkyl. More preferably, R17 is alkyl having 3 to 6 carbon atoms or cycloalkyl having 5 to 6 carbon atoms. Particularly preferred R17 groups include methyl, n-propyl, isopropyl, 1-hydroxy-2-methylprop-2-yl, n-butyl, tert-butyl, 3-thiomethylpropyl, 3-(thiomethoxy)but-1-yl, cyclohexyl, 4-trifluoromethybenzyl and 3,4,5-trimethoxybenzyl.
In still another preferred embodiment, this invention is directed to a compound of formula IV: 
wherein
R18 is selected from the group consisting of alkyl, substituted alkyl, cycloalkyl and substituted cycloalkyl;
R19 is selected from the group consisting of hydrogen, alkyl, substituted alkyl, cycloalkyl and substituted cycloalkyl; or R18 and R19 can be joined to form an alkylene or substituted alkylene group having from 2 to 10 carbon atoms;
R20 is selected from the group consisting of alkyl, substituted alkyl, cycloalkyl and substituted cycloalkyl; and pharmaceutically-acceptable salts thereof.
Preferably, R18 is alkyl or alkoxyalkyl (i.e., RO-alkyl-, where R is alkyl). Particularly preferred R18 groups include methyl and methoxyethyl. R19 is preferably hydrogen.
R20 is preferably selected from the group consisting of alkyl, substituted alkyl and cycloalkyl. More preferably, R20 is alkyl having 3 to 6 carbon atoms or cycloalkyl having 5 to 6 carbon atoms. Particularly preferred R20 groups include methyl, n-propyl, isopropyl, 1-hydroxy-2-methylprop-2-yl, n-butyl, tert-butyl, 3-thiomethylpropyl, 3-(thiomethoxy)but-1-yl, cyclohexyl, 4-trifluoromethybenzyl and 3,4,5-trimethoxybenzyl.
Particularly preferred 3,4,5-trisubstituted aryl nitrone compounds include those having the formulae shown in Tables I, II and III.
Accordingly, in another of its composition aspects, this invention is directed to each of the individual compounds:
xcex1-(4-acetoxy-3,5-di-tert-butylphenyl)-N-tert-butylnitrone
xcex1-(4-isobutanoyloxy-3,5-di-tert-butylphenyl)-N-tert-butylnitrone
xcex1-(4-n-butanoyloxy-3,5-di-tert-butylphenyl)-N-tert-butylnitrone
xcex1-(4-acetoxy-3,5-di-tert-butylphenyl)-N-isopropylnitrone
xcex1-(4-acetoxy-3,5-di-tert-butylphenyl)-N-1-hydroxy-2-methylprop-2-ylnitrone
xcex1-(4-n-pentanoyloxy-3,5-di-tert-butylphenyl)-N-tert-butylnitrone
xcex1-(4-acetoxy-3,5-di-tert-butylphenyl)-N-4-trifluoromethylbenzylnitrone
xcex1-(4-propionyloxy-3,5-di-tert-butylphenyl)-N-tert-butylnitrone
xcex1-(4-acetoxy-3,5-di-tert-butylphenyl)-N-methylnitrone
xcex1-(4-acetoxy-3,5-di-tert-butylphenyl)-N-3,4,5-trimethoxybenzylnitrone
xcex1-[4-(ethylaminocarbonyloxy)-3,5-di-tert-butylphenyl]-N-tert-butylnitrone
xcex1-[4-(n-propylaminocarbonyloxy)-3,5-di-tert-butylphenyl]-N-tert-butylnitrone
xcex1-[4-(n-butylaminocarbonyloxy)-3,5-di-tert-butylphenyl]-N-tert-butylnitrone
xcex1-[4-(2-ethoxycarbonyl)ethylaminocarbonyloxy)-3,5-di-tert-butylphenyl]-N-tert-butylnitrone
xcex1-[4-(2-ethoxycarbonyl)methylaminocarbonyloxy)-3,5-di-tert-butylphenyl]-N-tert-butylnitrone
xcex1-[4-methoxymethoxy-3,5-di-tert-butylphenyl)-N-tert-butylnitrone
xcex1-[4-(2-methoxy)ethoxymethoxy-3,5-di-tert-butylphenyl]-N-tert-butylnitrone
xcex1-(4-methoxymethoxy-3,5-di-tert-butylphenyl)-N-3-(thiomethoxy)but-1-ylnitrone
xcex1-(4-methoxymethoxy-3,5-di-tert-butylphenyl)-N-3-thiomethoxypropylnitrone
and pharmaceutically acceptable salts thereof.
In another of its composition aspects, this invention is directed to pharmaceutical compositions comprising a pharmaceutically acceptable carrier and a pharmaceutically effective amount of a compound of formula I: 
wherein R1-R4 are as defined above.
In additional composition aspects, this invention is directed to pharmaceutical compositions comprising a pharmaceutically acceptable carrier and a pharmaceutically effective amount of a compound of formula II, III or IV above.
Among other properties, the 3,4,5-trisubstituted aryl nitrone compounds of this invention are believed to inhibit the induction of cyclooxygenase associated with prostagladin E2 (PGE2) synthesis and inflammation. Compounds having such properties are useful for reducing inflammation, including inflammation resulting from arthritis and related inflammatory conditions.
Accordingly, in one of its method aspects, this invention is directed to a method for treating a mammal with an inflammation-related condition which method comprises administering to said mammal a pharmaceutical composition comprising a pharmaceutically acceptable carrier and an effective inflammation-reducing amount of a compound of formula I, II, III or IV above.
In preferred embodiments of this invention, the inflammation-related condition treated in the above methods is rheumatoid arthritis, osteoarthritis, ankylosing spondylitis, systemic lupus erythematosus, psoriatic arthitis, and the like.
For the purposes of this invention, the 3,4,5-trisubstituted aryl nitrone compounds of formula I are named using conventional nitrone nomenclature, i.e., the carbon atom of the carbon-nitrogen double bond (Cxe2x95x90N) is designated the xcex1-position and substituents on the nitrogen atom of the carbon-nitrogen double bond are given the N- prefix.
In some cases, the 3,4,5,-trisubstituted aryl nitrones of this invention may contain one or more chiral centers. Typically, such compounds will be prepared as a racemic mixture. If desired, however, such compounds can be prepared or isolated as pure stercoisomers, i.e., as individual cantiomers or diastereomers, or as stercoisomer-enriched mixtures. All such stereoisomers (and enriched mixtures) of the 3,4,5-trisubstituted aryl nitrones of formula I are included within the scope of this invention. Pure stercoisomers (or enriched mixtures) may be prepared using, for example, optically active starting materials or stereoselective reagents well known in the art. Alternatively, racemic mixtures of such compounds can be separated using, for example, chiral column chromatography, chiral resolving agents and the like.
Additionally, all geometric isomers of the nitrone compounds of formula I are included within the scope of this invention including, for example, all isomers (i.e. E and Z isomers) of the carbon-nitrogen double bond of the nitrone functionality.
Definitions
When describing the 3,4,5-trisubstituted aryl nitrones, pharmaceutical compositions and methods of this invention, the following terms have the following meanings unless otherwise specified.
xe2x80x9cAcylxe2x80x9d refers to the group xe2x80x94C(O)R where R is hydrogen, alkyl, aryl or cycloalkyl.
xe2x80x9cAcylaminoxe2x80x9d refers to the group xe2x80x94NRC(O)R where each R is independently hydrogen, alkyl, aryl or cycloalkyl.
xe2x80x9cAcyloxyxe2x80x9d refers to the group xe2x80x94OC(O)R where R is hydrogen, alkyl, aryl or cycloalkyl.
xe2x80x9cAlkenylxe2x80x9d refers to a monovalent branched or unbranched unsaturated hydrocarbon group preferably having from 2 to 10 carbon atoms and more preferably 2 to 6 carbon atoms and having at least 1 and preferably from 1-2 sites of carbon-carbon double bond unsaturation. Preferred alkenyl groups include ethenyl (xe2x80x94CHxe2x95x90CH2), n-propenyl (xe2x80x94CH2CHxe2x95x90CH2), isopropenyl (xe2x80x94C(CH3)xe2x95x90CH2), and the like.
xe2x80x9cSubstituted alkenylxe2x80x9d refers to an alkenyl group having from 1 to 5 substituents, and preferably from 1 to 3 substiutents, selected from the group consisting of acyl, acylamino, acyloxy, alkoxy, substituted alkoxy, alkoxycarbonyl, alkoxycarbonylamino, amino, substituted amino, aminocarbonyl, aminocarbonylamino, aminocarbonyloxy, aryl, aryloxy, azido, carboxyl, cyano, cycloalkyl, substituted cycloalkyl, halogen, hydroxyl, keto, nitro, thioalkoxy, substituted thioalkoxy, thioaryloxy, thioketo, thiol, alkylxe2x80x94S(O)xe2x80x94, arylxe2x80x94S(O)xe2x80x94, alkylxe2x80x94S(O)2xe2x80x94 and arylxe2x80x94S(O)2xe2x80x94.
xe2x80x9cAlkoxyxe2x80x9d refers to the group xe2x80x94OR where R is alkyl. Preferred alkoxy groups include, by way of example, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, tert-butoxy, sec-butoxy, n-pentoxy, n-hexoxy, 1,2-dimethylbutoxy, and the like.
xe2x80x9cSubstituted alkoxyxe2x80x9d refers to an alkoxy group having from 1 to 5 substituents, and preferably from 1 to 3 substituents, selected from the group consisting of acyl, acylamino, acyloxy, alkoxy, substituted alkoxy, alkoxycarbonyl, alkoxycarbonylamino, amino, substituted amino, aminocarbonyl, aminocarbonylamino, aminocarbonyloxy, aryl, aryloxy, azido, carboxyl, cyano, cycloalkyl, substituted cycloalkyl, halogen, hydroxyl, keto, nitro, thioalkoxy, substituted thioalkoxy, thioaryloxy, thioketo, thiol, alkylxe2x80x94S(O)xe2x80x94, arylxe2x80x94S(O)xe2x80x94, alkylxe2x80x94S(O)2xe2x80x94 and arylxe2x80x94S(O)2xe2x80x94.
xe2x80x9cAlkoxycarbonylxe2x80x9d refers to the group xe2x80x94C(O)OR where R is alkyl or cycloalkyl.
xe2x80x9cAlkoxycarbonylaminoxe2x80x9d refers to the group xe2x80x94NRC(O)ORxe2x80x2 where R is hydrogen, alkyl, aryl or cycloalkyl, and Rxe2x80x2 is alkyl or cycloalkyl.
xe2x80x9cAlkylxe2x80x9d refers to a monovalent branched or unbranched saturated hydrocarbon group preferably having from 1 to about 10 carbon atoms, more preferably from 1 to 8 carbon atoms and still more preferably 1 to 6 carbon atoms. This term is exemplified by groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-hexyl, n-octyl, tert-octyl and the like. The term xe2x80x9clower alkylxe2x80x9d refers to an alkyl group having from 1 to 6 carbon atoms.
xe2x80x9cSubstituted alkylxe2x80x9d refers to an alkyl group having from 1 to 5 substituents, and preferably from 1 to 3 substituents, selected from the group consisting of acyl, acylamino, acyloxy, alkoxy, substituted alkoxy, alkoxycarbonyl, alkoxycarbonylamino, amino, substituted amino, aminocarbonyl, aminocarbonylamino, aminocarbonyloxy, aryl, aryloxy, azido, carboxyl, cyano, cycloalkyl, substituted cycloalkyl, halogen, hydroxyl, keto, nitro, thioalkoxy, substituted thioalkoxy, thioaryloxy, thioketo, thiol, alkylxe2x80x94S(O)xe2x80x94, arylxe2x80x94S(O)xe2x80x94, alkylxe2x80x94S(O)2xe2x80x94 and arylxe2x80x94S(O)2xe2x80x94.
xe2x80x9cAlkylenexe2x80x9d refers to a divalent branched or unbranched saturated hydrocarbon group preferably having from 1 to 10 carbon atoms and more preferably from 1 to 6 carbon atoms. This term is exemplified by groups such as methylene (xe2x80x94CH2xe2x80x94), ethylene (xe2x80x94CH2CH2xe2x80x94), the propylene isomers (e.g., xe2x80x94CH2CH2CH2xe2x80x94 and xe2x80x94CH(CH3)CH2xe2x80x94) and the like.
xe2x80x9cSubstituted alkylenexe2x80x9d refers to an alkylene group having from 1 to 5 substituents, and preferably from 1 to 3 substituents, selected from the group consisting of acyl, acylamino, acyloxy, alkoxy, substituted alkoxy, alkoxycarbonyl, alkoxycarbonylamino, amino, substituted amino, aminocarbonyl, aminocarbonylamino, aminocarbonyloxy, aryl, aryloxy, azido, carboxyl, cyano, halogen, hydroxyl, keto, nitro, thioalkoxy, substituted thioalkoxy, thioatyloxy, thioketo, thiol, alkylxe2x80x94S(O)xe2x80x94, arylxe2x80x94S(O)xe2x80x94, alkylxe2x80x94S(O)2xe2x80x94 and arylxe2x80x94S(O)2xe2x80x94.
xe2x80x9cAlkynylxe2x80x9d refers to a monovalent branched or unbranched unsaturated hydrocarbon group preferably having from 2 to 10 carbon atoms and more preferably 2 to 6 carbon atoms and having at least 1 and preferably from 1-2 sites of carbon-carbon triple bond unsaturation. Preferred alkynyl groups include ethynyl (xe2x80x94Cxe2x89xa1CH), propargyl (xe2x80x94CH2Cxe2x89xa1CH) and the like.
xe2x80x9cSubstituted alkynylxe2x80x9d refers to an alkynyl group having from 1 to 5 substituents, and preferably from 1 to 3 substituents, selected from the group consisting of acyl, acylamino, acyloxy, alkoxy, substituted alkoxy, alkoxycarbonyl, alkoxycarbonylamino, amino, substituted amino, aminocarbonyl, aminocarbonylamino, aminocarbonyloxy, aryl, aryloxy, azido, carboxyl, cyano, cycloalkyl, substituted cycloalkyl, halogen, hydroxyl, keto, nitro, thioalkoxy, substituted thioalkoxy, thioaryloxy, thioketo, thiol, alkylxe2x80x94S(O)xe2x80x94, arylxe2x80x94S(O)xe2x80x94, alkylxe2x80x94S(O)2xe2x80x94 and arylxe2x80x94S(O)2xe2x80x94.
xe2x80x9cAminoxe2x80x9d refers to the group xe2x80x94NH2.
xe2x80x9cSubstituted aminoxe2x80x9d refers to the group xe2x80x94N(R)2 where each R is independently selected from the group consisting of hydrogen, alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl, cycloalkyl, substituted cycloalkyl, and where both R groups are joined to form an alkylene group. When both R groups are hydrogen, xe2x80x94N(R)2 is an amino group.
xe2x80x9cAminocarbonylxe2x80x9d refers to the group xe2x80x94C(O)NRR where each R is independently hydrogen, alkyl, aryl and cycloalkyl, or where the R groups are joined to form an alkylene group.
xe2x80x9cAminocarbonylaminoxe2x80x9d refers to the group xe2x80x94NRC(O)NRR where each R is independently hydrogen, alkyl, aryl or cycloalkyl, or where two R groups are joined to form an alkylene group.
xe2x80x9cAminocarbonyloxyxe2x80x9d refers to the group xe2x80x94OC(O)NRR where each R is independently hydrogen, alkyl, aryl or cycloalkyl, or where the R groups are joined to form an alkylene group.
xe2x80x9cArylxe2x80x9d refers to an unsaturated aromatic carbocyclic group of from 6 to 14 carbon atoms having a single ring (e.g., phenyl) or multiple condensed lings (e.g., naphthyl or anthryl). Preferred aryls include phenyl, naphthyl and the like. Unless otherwise constrained by the definition for the individual substituent, such aryl groups can optionally be substituted with from 1 to 5 substituents, preferably 1 to 3 substituents, selected from the group consisting of acyl, acylamino, acyloxy, alkenyl, substituted alkenyl, alkoxy, substituted alkoxy, alkoxycarbonyl, alkyl, substituted alkyl, alkynyl, substituted alkynyl, amino, substituted amino, aminocarbonyl, aminocarbonylamino, aminocarbonyloxy, aryl, aryloxy, azido, carboxyl, cyano, cycloalkyl, substituted cycloalkyl, halogen, hydroxyl, nitro, thioalkoxy, substituted thioalkoxy, thioaryloxy, thiol, alkylxe2x80x94S(O)xe2x80x94, arylxe2x80x94S(O)xe2x80x94, alkylxe2x80x94S(O)2xe2x80x94 and arylxe2x80x94S(O)2xe2x80x94.
xe2x80x9cAryloxyxe2x80x9d refers to the group xe2x80x94OR where R is aryl.
xe2x80x9cCycloalkylxe2x80x9d refers to a cyclic alkyl group of from 3 to 10 carbon atoms having a single cyclic ring or multiple condensed or bridged rings which can be optionally substituted with from 1 to 3 alkyl groups. Such cycloalkyl groups include, by way of example, single ring structures such as cyclopropyl, cyclobutyl, cyclopentyl, cyclooctyl, 1-methylcyclopropyl, 2-methylcyclopentyl, 2-methylcyclooctyl, and the like, or multiple or bridged ring structures such as adamanitanyl and the like. The term xe2x80x9clower cycloalkylxe2x80x9d refers to a cycloalkyl group having from 3 to 6 carbon atoms.
xe2x80x9cSubstituted cycloalkylxe2x80x9d refers to a cycloalkyl group having from 1 to 5 substituents, and preferably from 1 to 3 substituents, selected from the group consisting of acyl, acylamino, acyloxy, alkoxy, substituted alkoxy, alkoxycarbonyl, alkoxycarbonylamino, amino, substituted amino, aminocarbonyl, aminocarbonylamino, aminocarbonyloxy, aryl, aryloxy, azido, carboxyl, cyano, cycloalkyl, substituted cycloalkyl, halogen, hydroxyl, keto, nitro, thioalkoxy, substituted thioalkoxy, thioaryloxy, thioketo, thiol, alkylxe2x80x94S(O)xe2x80x94, arylxe2x80x94S(O)xe2x80x94, alkylxe2x80x94S(O)2xe2x80x94 and arylxe2x80x94S(O)2xe2x80x94.
xe2x80x9cycloalkoxyxe2x80x9d refers to the group xe2x80x94OR where R is cycloalkyl. Such cycloalkoxy groups include, by way of example, cyclopentoxy, cyclohexoxy and the like.
xe2x80x9cCycloalkenylxe2x80x9d refers to a cyclic alkenyl group of from 4 to 10 carbon atoms having a single cyclic ring and at least one point of internal unsaturation which can be optionally substituted with from 1 to 3 alkyl groups. Examples of suitable cycloalkenyl groups include, for instance, cyclopent-3-enyl, cyclohex-2-enyl, cyclooct-3-enyl and the like.
xe2x80x9cSubstituted cycloalkenylxe2x80x9d refers to a cycloalkenyl group having from 1 to 5 substituents, and preferably from 1 to 3 substituents, selected from the group consisting of acyl, acylamino, acyloxy, alkoxy, substituted alkoxy, alkoxycarbonyl, alkoxycarbonylamino, amino, substituted amino, aminocarbonyl, aminocarbonylamino, aminocarbonyloxy, aryl, aryloxy, azido, carboxyl, cyano, cycloalkyl, substituted cycloalkyl, halogen, hydroxyl, keto, nitro, thioalkoxy, substituted thioalkoxy, thioaryloxy, thioketo, thiol, alkylxe2x80x94S(O)xe2x80x94, arylxe2x80x94S(O)xe2x80x94, alkylxe2x80x94S(O)2xe2x80x94 and arylxe2x80x94S(O)2xe2x80x94.
xe2x80x9cHaloxe2x80x9d or xe2x80x9chalogenxe2x80x9d refers to fluoro, chloro, bromo and iodo. Preferred halo groups are either fluoro or chloro.
xe2x80x9cHydroxylxe2x80x9d refers to the group xe2x80x94OH.
xe2x80x9cKetoxe2x80x9d or xe2x80x9coxoxe2x80x9d refers to the group xe2x95x90O.
xe2x80x9cNitroxe2x80x9d refers to the group xe2x80x94NO2.
xe2x80x9cThioalkoxyxe2x80x9d refers to the group xe2x80x94SR where R is alkyl.
xe2x80x9cSubstituted thioalkoxyxe2x80x9d refers to a thioalkoxy group having from 1 to 5 substituents, and preferably from 1 to 3 substituents, selected from the group consisting of acyl, acylamino, acyloxy, alkoxy, substituted alkoxy, alkoxycarbonyl, alkoxycarbonylamino, amino, substituted amino, aminocarbonyl, aminocarbonylamino, aminocarbonyloxy, aryl, aryloxy, azido, carboxyl, cyano, cycloalkyl, substituted cycloalkyl, halogen, hydroxyl, keto, nitro, thioalkoxy, substituted thioalkoxy, thioaryloxy, thioketo, thiol, alkylxe2x80x94S(O)xe2x80x94, arylxe2x80x94S(O)xe2x80x94, alkylxe2x80x94S(O)2xe2x80x94 and arylxe2x80x94S(O)2xe2x80x94.
xe2x80x9cThioaryloxyxe2x80x9d refers to the group xe2x80x94SR where R is aryl.
xe2x80x9cThioketoxe2x80x9d refers to the group xe2x95x90S.
xe2x80x9cThiolxe2x80x9d refers to the group xe2x80x94SH.
xe2x80x9cPharmaceutically-acceptable saltxe2x80x9d refers to any salt of a compound of this invention which retains its biological properties and which is not biologically or otherwise undesirable. Such salts may be derived from a variety of organic and inorganic counter-ions well known in the art and include, by way of example illustration, sodium, potassium, calcium, magnesium, ammonium, tetraalkylammonium, and the like; and when the molecule contains a basic functionality, salts of organic or inorganic acids, such as hydrochloride, hydrobromide, tartrate, mesylate, acetate, maleate, oxalate and the like. The term xe2x80x9cpharmaceutically-acceptable cationxe2x80x9d refers to a pharmaceutically acceptable cationic counter-ion of an acidic functional group. Such cations are exemplified by sodium, potassium, calcium, magnesium, ammonium, tetraalkylammonium cations, and the like.
General Synthetic Procedures
The 3,4,5-trisubstituted aryl nitrones of this invention can be prepared from readily available starting materials using the following general methods and procedures. It will be appreciated that where typical or preferred process conditions (i.e., reaction temperatures, times, mole ratios of reactants, solvents, pressures, etc.) are given, other process conditions can also be used unless otherwise stated. Optimum reaction conditions may vary with the particular reactants or solvent used, but such conditions can be determined by one skilled in the art by routine optimization procedures.
Additionally, as will be apparent to those skilled in the art, conventional protecting groups may be necessary to prevent certain functional groups from undergoing undesired reactions. The choice of a suitable protecting group for a particular functional group as well as suitable conditions for protection and deprotection are well known in the art. For example, numerous protecting groups, and their introduction and removal, are described in T. W. Greene and G. M. Wuts, Protecting Groups in Organic Synthesis, Second Edition, Wiley, New York, 1991, and references cited therein.
In a preferred method of synthesis, the 3,4,5-trisubstituted aryl nitrones of this invention are prepared by coupling an aryl carbonyl compound of formula V: 
wherein R1, R2 and R3 are as defined above, with a hydroxylamine of formula VI:
HOxe2x80x94NHxe2x80x94R4xe2x80x83xe2x80x83VI
wherein R4 is as defined above, under conventional reaction conditions.
This coupling reaction is typically conducted by contacting the aryl carbonyl compound V with at least one equivalent, preferably about 1.1 to about 2 equivalents, of hydroxylamine VI in an inert polar solvent such as methanol, ethanol, 1,4-dioxane, tetrahydrofuran, dimethyl sulfoxide, dimethylformamide and the like. This reaction is preferably conducted at a temperature of from about 0xc2x0 C. to about 100xc2x0 C. for about 1 to about 48 hours. Optionally, a catalytic amount of an acid, such as hydrochloric acid, acetic acid, p-toluenesulfonic acid, silica gel and the like, may be employed in this reaction. When R1 in formula V is xe2x80x94C(O)R3, at least two equivalents of hydroxylamine VI are employed in this coupling reaction. Upon completion of the reaction, the 3,4,5-trisubstituted aryl nitrone of formula I is recovered by conventional methods including precipitation, chromatographic separation, filtration, distillation, sublimation, and the like.
The aryl carbonyl compounds of formula V employed in the a above-described coupling reaction are either known compounds or compounds that can be prepared from known compounds by conventional procedures. For example, aryl carbonyl compounds of formula V where R1 is xe2x80x94C(O)R5 are readily prepared by acylation of the corresponding 4-hydroxy derivative. For example, in a preferred embodiment, 3,5-di-tert-butyl-4-hydroxybenzaldehyde (available from Aldrich Chemical Co., 1001 W. St. Paul Avenue, Milwaukee, Wis., USA 53233-2641) is acetylated by contacting the benzaldehyde with excess acetic anhydride in the presence of an acid catalyst, such as perchlolic acid, followed by hydrolysis of the intermediate acetal, to afford 4-acetoxy-3,5-di-tert-butylbenzaldehyde. Other carboxylic anhydrides may also be employed in this reaction including, by way of example, propionic anhydride, butyric anhydride, isobutyric anhydride and the like. Alternatively, such compounds can be prepared by acylation of the 4-hydroxy compound with other acylating agents, such as acyl halides, under conventional reaction conditions. The acyl halides employed in this reaction are preferably acyl chlorides or acyl bromides, such as acetyl chloride, acetyl bromide, propionyl chloride, n-butyryl chloride, isobutyryl chloride and the like. Typically, this reaction is conducted in the presence of a trialkylamine, such as triethylamine, to neutralize the acid generated during the reaction.
Similarly, the aryl carbonyl compounds of formula V where R1 is xe2x80x94-C(O)NR6R7 are readily prepared by reaction of the corresponding 4-hydroxy derivative with an isocyanate (i.e., R6R7Nxe2x95x90Cxe2x95x90O). For example, in a preferred embodiment, 3,5-di-tert-butyl-4-hydroxybenzaldehyde is reacted with ethylisocyanate to afford 4-(ethylaminocarbonyloxy)-3,5-di-tert-butylbenizaldelhyde. Typically, this reaction is conducted at ambient temperature in an inert diluent, such as N,N-dimethylformamide, in the presence of an excess of a trialkylamine, such as triethylamine and the like. Other isocyantes may be employed in this reaction including, by way of illustration, n-propylisocyanate, n-butylisocyanate and the like.
Additionally, the aryl carbonyl compounds of formula V where R1 is xe2x80x94CHR9xe2x80x94Xxe2x80x94R8 are readily prepared by reacting the corresponding 4-hydroxy derivative with a compound of the formula Lxe2x80x94CHR9xe2x80x94Xxe2x80x94R8, where L is a leaving group, such as a halogen or a sulfonate ester, and R8, R9 and X are as defined herein. Typically, this reaction is conducted by contacting the 4-hydroxy derivative with an excess of the alkylating agent in the presence of an equimolar amount of a trialkylamine, such as N,N-diisopropylethylamine, in an inert diluent such as 1,2-dichloroethane. Preferred alkylating agents for use in this reaction include, by way of example, methoxymethyl chloride and 2-methoxyethoxymethyl (MEM) chloride.
The hydroxylamine compounds of formula VI above are also known compounds or compounds which can be prepared from known compounds by conventional procedures. Typically, the hydroxylamine compounds of formula VI are prepared by reducing the corresponding nitro compound (i.e., R4xe2x80x94NO2, wherein R4 is as defined above) using a suitable reducing agent such as activated zinc/acetic acid, activated zinc/ammonium chloride or an aluminum/mercury amalgam. This reaction is typically conducted at a temperature ranging from about 15xc2x0 C. to about 100xc2x0 C. for about 0.5 to 12 hours, preferably about 2 to 6 hours, in an aqueous reaction media, such as an alcohol/water mixture in the case of the zinc reagents or an ether/water mixture in the case of the aluminum amalgams. Aliphatic nitro compounds (in the form of their salts) can also be reduced to hydroxylamines using borane in tetrahydrofuran. Since some hydroxylamines have limited stability, such compounds are generally prepared immediately prior to reaction with the aryl carbonyl compound of formula V.
Preferred hydroxylamines for use in this invention include, but are not limited to, N-isopropylhydroxylamine, N-n-propylhydroxylamine, N-n-butylhydroxylamine, N-tert-butylhydroxylamine, N-cyclohexylhydroxylamine and the like.
Pharmaceutical Compositions
When employed as pharmaceuticals, the 3,4,5-trisubstituted aryl nitrones of this invention are typically administered in the form of a pharmaceutical composition. Such compositions can be prepared using procedures well known in the pharmaceutical art and comprise at least one active compound.
Generally, the compounds of this invention are administered in a pharmaceutically effective amount. The amount of the compound actually administered will typically be determined by a physician, in the light of the relevant circumstances, including the condition to be treated, the chosen route of administration, the actual compound administered, the age, weight, and response of the individual patient, the severity of the patient""s symptoms, and the like.
The pharmaceutical compositions of this invention can be administered by any suitable routes including, by way of illustration, oral, topical, rectal, transdermal, subcutaneous, intravenous, intramuscular, intranasal, and the like. Depending on the intended route of delivery, the compounds of this invention are preferably formulated as either oral, topical or injectable compositions.
Pharmaceutical compositions for oral administration can take the form of bulk liquid solutions or suspensions, or bulk powders. More commonly, however, such compositions are presented in unit dosage forms to facilitate accurate dosing. The term xe2x80x9cunit dosage formsxe2x80x9d refers to physically discrete units suitable as unitary dosages for human subjects and other mammals, each unit containing a predetermined quantity of active material calculated to produce the desired therapeutic effect, in association with a suitable pharmaceutical excipient. Typical unit dosage forms include prefilled, premeasured ampules or syringes of the liquid compositions or pills, tablets, capsules or the like in the case of solid compositions. In such compositions, the nitrone compound is usually a minor component (from about 0.1 to about 50% by weight or preferably from about 1 to about 40% by weight) with the remainder being various vehicles or carriers and processing aids helpful for forming the desired dosing form.
Liquid forms suitable for oral administration may include a suitable aqueous or nonaqueous vehicle with buffers, suspending and dispensing agents, colorants, flavors and the like. Solid forms may include, for example, any of the following ingredients, or compounds of a similar nature: a binder such as microcrystalline cellulose, gum tragacanth or gelatin; an excipient such as starch or lactose, a disintegrating agent such as alginic acid, Primogel, or corn starch; a lubricant such as magnesium stearate; a glidant such as colloidal silicon dioxide; a sweetening agent such as sucrose or saccharin; or a flavoring agent such as peppermint, methyl salicylate, or orange flavoring.
Topical compositions are typically formulated as a topical ointment or cream containing the active ingredient(s), generally in an amount ranging from about 0.01 to about 20% by weight, preferably from about 0.1 to about 10% by weight, and more preferably from about 0.5 to about 15% by weight. When formulated as an ointment, the active ingredients will typically be combined with either a paraffinic or a water-miscible ointment base. Alternatively, the active ingredients may be formulated in a cream with, for example, an oil-in-water cream base. Such topical formulations are well-known in the art and generally include additional ingredients to enhance the dermal penetration or stability of the active ingredients or the formulation. All such known topical formulations and ingredients are included within the scope of this invention.
The compounds of this invention can also be administered by a transdermal device. Accordingly, topical administration can be accomplished using a patch either of the reservoir or porous membrane type or of a solid matrix variety.
Injectable compositions are typically based upon injectable sterile saline or phosphate-buffered saline or other injectable carriers known in the art. As before, the 3,4,5-trisubstituted aryl nitrone compound in such compositions is typically a minor component, often being from about 0.05 to 10% by weight with the remainder being the injectable carrier and the like.
The above-described components for orally and topically administrable or injectable compositions are merely representative. Other materials as well as processing techniques and the like are set forth in Part 8 of Remington""s Pharmaceutical Sciences, 18th edition, 1990, Mack Publishing Company, Easton, Pa., 18042, which is incorporated herein by reference.
The compounds of this invention can also be administered in sustained release forms or from sustained release drug delivery systems. A description of representative sustained release materials can be found in the incorporated materials in Remington""s Pharmaceutical Sciences. 
The following formulation examples illustrate representative pharmaceutical compositions of this invention. The present invention, however, is not limited to the following pharmaceutical compositions.
Formulation 1xe2x80x94Tablets
A compound of formula I is admixed as a dry powder with a dry gelatin binder in an approximate 1:2 weight ratio. A minor amount of magnesium stearate is added as a lubricant. The mixture is formed into 240-270 mg tablets (80-90 mg of active nitrone compound per tablet) in a tablet press.
Formulation 2xe2x80x94Capsules
A compound of formula I is admixed as a dry powder with a starch diluent in an approximate 1:1 weight ratio. The mixture is filled into 250 mg capsules (125 mg of active nitrone compound per capsule).
Formulation 3xe2x80x94Liquid
A compound of formula 1 (125 mg), sucrose (1.75 g) and xanthan gum (4 mg) are blended, passed through a No. 10 mesh U.S. sieve, and then mixed with a previously made solution of microcrystalline cellulose and sodium carboxymethyl cellulose (11:89, 50 mg) in water. Sodium benzoate (10 mg), flavor, and color are diluted with water and added with stirring. Sufficient water is then added to produce a total volume of 5 mL.
Formulation 4xe2x80x94Injection
The compound of formula I is dissolved in a buffered sterile saline injectable aqueous medium to a concentration of approximately 5 mg/mL.
Formulation 5xe2x80x94Ointment
Stearyl alcohol (250 g) and white petrolatum (250 g) are melted at about 75xc2x0 C. and then a mixture of a compound of formula 1 (50 g), methylparaben (0.25 g), propylparaben (0.15 g), sodium lauryl sulfate (10 g), and propylene glycol (120 g) dissolved in water (about 370 g) is added and the resulting mixture is stirred until it congeals.
Compound Utility
Among other properties, the 3,4,5-trisubstituted aryl nitrones of this invention have been discovered to inhibit the induction of inducible cylcooxygenase (COX-2) and/or to inhibit the release of physiologically active leukotrienes and/or to be effective in various in vivo arthritis models. Accordingly, the compounds and pharmaceutical compositions of this invention find use as therapeutics for treating inflammation-related conditions in mammals including humans.
In particular, the compounds of this invention have been discovered to effectively inhibit the induction of inducible cyclooxygenase (COX-2), the release of which results in prostagladin E2 (PGE2) synthesis. PGE2 is produced by the enzyme COX as part of the arachidonic acid pathway. The enzyme COX is now known to exist in two forms, COX-1 and COX-2. COX-1 is a constitutive form of the enzyme found in most tissues and organs. COX-2, on the other band, is an inducible form of the enzyme associated with the production of PGE2 and inflammation. Without being limited to theory, it is believed that selective inhibition of COX-2 formation will provide therapeutic agents which effectively reduce inflammation with fewer or none of the side effects associated with inhibition of COX-1 and/or COX-2. Since the compounds of this invention have been discovered to inhibit the release PGE2, such compounds are useful for treating diseases or conditions characterized by an overproduction or a dysregulated production of prostagladin E2 including many inflammatory conditions.
Among the inflammation-related conditions which may be treated with the 3,4,5-trisubstituted aryl nitrone compounds and pharmaceutical compositions of this invention are various forms of arthritis, including but not limited to, rheumatoid arthritis, osteoarthritis, ankylosing spondylitis, systemic lupus erythematosus, psoriatic arthritis, and the like. Other inflammation-related conditions include, by way of illustration, inflammatory bowel disease (IBD), septic shock, erythema nodosum leprosy, septicemia, uveitis, adult respiratory distress syndrome (ARDS), organ rejection, neuro-inflammatory conditions, cardio-inflammatory conditions and the like.
As discussed above, the compounds described herein are suitable for use in a variety of drug delivery systems. Injection dose levels for treating inflammation-related conditions range from about 0.1 mg/kg/hour to at least 10 mg/kg/hour, all for from about 1 to about 120 hours and especially 24 to 96 hours. A preloading bolus of from about 0.1 mg/kg to about 10 mg/kg or more may also be administered to achieve adequate steady state levels. The maximum total dose is not expected to exceed about 2 g/day for a 40 to 80 kg human patient.
For the treatment of long-term conditions, such as arthritis, the regimen for treatment may stretch over many months or years so oral dosing is preferred for patient convenience and tolerance. With oral dosing, one to five and especially two to four and typically three oral doses per day are representative regimens. Using these dosing patterns, each dose provides from about 0.1 to about 20 mg/kg of the nitrone, with preferred doses each providing from about 0.1 to about 10 mg/kg and especially about 1 to about 5 mg/kg.
The compounds of this invention can be administered as the sole active agent or they can be administered in combination with other active agents, such as cyclooxygenase inhibitors, 5-lipoxygenase inhibitors, non-steroidal antiinflammatory drugs (NSAIDs), steroids, peripheral analgesic agents such as zomepirac, diflunisol, and the like, and other active nitrone derivatives.
The novel 3,4,5-trisubstituted aryl nitrones of this invention also find use as analytical reagents, i.e. as spin traps, for detecting unstable free radicals using electron spin resonance (ESR) spectroscopy and related techniques. When used as analytical reagents, the nitrone compounds of this invention are typically contacted with the radical to be studied in solution and an ESR spectrum generated in a conventional manner. In particular, the nitrones of this invention may be used to detect and identify free radicals in biological systems. Any ESR spectrometer, such as a JEOL JES-FE3XG spectrometer, may be employed in these experiments. Typically, the solution containing the spin-trap will be deoxygenated by, for example, bubbling argon or nitrogen through the solution before the ESR experiment is conducted. Preferably, an excess of the nitrone is used in such ESR experiments.
The actual experimental procedures employed in the spin-trapping experiment will depend on a number of factors, such as the manner of radical production, the inertness of the solvent and reagents with respect to the spin trap, the lifetime of the spin adduct and the like. Spin trapping procedures are well known in the art and the exact procedure employed can be determined by those skilled in the art. Typical procedures and apparatus for conducting spin trapping experiments are described, for example, in C. A. Evans, xe2x80x9cSpin Trappingxe2x80x9d, Aldrichimica Acta, (1979), 12(2), 23-29, and references cited therein.